1. Field of the Invention
The present invention relates to a method for producing a lithium secondary battery.
More particularly, the present invention relates to a method for producing a lithium secondary battery, which involves simultaneously bonding cathode plates and anode plates cut in a uniform size to both surfaces of a separation film which runs continuously in a vertical direction, in such a fashion that the electrode plates on each surface of the separation film are uniformly spaced apart from one another, and folding the separation film several times to alternate the cathode plates and the anode plates, thereby being capable of achieving a simplified and consistent production process while readily providing a cell having various shapes, sizes and a desired capacity.
2. Description of the Related Art
Such lithium secondary batteries of a lamination type having the above-mentioned construction are well known. Typically, the batteries are produced by bonding a plurality of cathode plates to one surface of a separation film which runs in a horizontal direction, bonding a plurality of anode plates to other surface of the separation film, in which the anode plates are positioned opposite to the cathode plates, and folding the separation film several times so that the cathode plates and anode plates are arranged alternately, as shown in FIG. 2.
In accordance with the conventional method in which processes are carried out in a horizontal fashion, however, the bonding process and the lamination process are carried out, in separate fashion, for respective surfaces of the separation film on which the cathode plates and the anode plates are to be bonded. As a result, the coating process of the adhesive, the bonding process of cathode plates or anode plates and the laminating process have to be conducted twice, leading a degradation in process efficiency. Furthermore, since a solenoid valve type nozzle is used for an injection of the adhesive, it is difficult to control an amount of the injected adhesive. In addition, the spreading degree of the adhesive is varied with the viscosity of the adhesive. Also, a string phenomenon may occur. Accordingly, the production of batteries having a poor quality is increased.
Therefore, an object of the invention is to solve the above-mentioned problems involved in the prior art, and to provide a method for producing a lithium secondary battery by producing the lithium secondary battery in a vertical fashion so as to increase the efficiency of producing the battery and lower the defective proportion of the battery.
In accordance with the present invention, a method for producing a lithium secondary battery is provided, in which the method comprises:
(1) unwinding a separation film for insulating electrodes by a roller;
(2) simultaneously coating an adhesive by an air injector on both surfaces of the separation film at regions where cathode plates and anode plates are to be attached to the separation film;
(3) simultaneously bonding the cathode plates and the anode plates respectively on the surfaces of the separation film while allowing the electrode plates on each surface of the separation film to be uniformly spaced apart from one another;
(4) laminating the bonded cathode plates and anode plates; and
(5) laminating the separation film bonded with the cathode plates and the anode plates so that the cathode plates and the anode plates are arranged alternately.
The anode plates used according to the present invention are prepared by coating an anode active material on a metal foil such as aluminum, drying the metal foil, and cutting the dried metal foil to have a desired size. The anode active material that can be used in the present invention includes, but is not limited to, a material, such as LiCO2, LiMn2O4, having a spinel or layered structure. Similarly, the cathode plates used according the present invention are prepared by coating a cathode active material on a metal foil such as copper, drying the metal foil, and cutting the dried metal foil to have a desired size. The cathode active material that can be used in the present invention includes, but is not limited to, graphite or carbon-based materials treated to have an electrochemical property, typically carbon materials based on mesocarbon microbeads (MCMB) and meso-phase pitch carbon film, etc.
As the separation film, single layer or multi-layered porous polymer films composed of polyethylene or polypropylene can be used. The adhesive adapted to attach cathode plates or anode plates is coated on the surfaces of the separation film by using an air injector. The air injector which applies the printing principal of inkjet marking is adapted to inject the adhesive through a nozzle by using compressed air so that the adhesive can be coated on the both surfaces of the separation film in a vertical fashion. When using the nozzle of the air injector according to the present invention, the injected adhesive has a ring shape, whereby the contact area between the adhesive layer and the electrode plate and the thickness of the adhesive layer can be reduced. Also, an excessive overcoating of the adhesive can be prohibited. Therefore, it is possible to achieve a reduction in string phenomenon and an improvement in electronic conductivity.
Preferably, the nozzle of the air injector has an inner diameter of 50 to 300 xcexcm.